Several methods for absorbing carbon dioxide gas have been reported. Specifically, chemical adsorption methods such as a method using a monoethanolamine aqueous solution (see, for example, Patent Document 1: Japanese Patent No. 2809368), a method using a tertiary amine (see, for example, Patent Document 2: Japanese Patent Application Laid-open No. 2003-261315), and a method using a porous powder having calcium hydroxide as a main component thereof (see, for example, Patent Document 3: Japanese Patent Application Laid-open No. 5-184864), and a solid adsorption method using a zeolite or the like (see, for example, Patent Document 4: Japanese Patent Application Laid-open No. 2004-344703) have been reported.
In the method for recovering carbon dioxide using a monoethanolamine aqueous solution or a tertiary amine, it is known that after the recovery, in a step of subjecting the absorbed carbon dioxide to decarbonation, the amine compound is entrained in the carbon dioxide; there has been reported a method in which, to remove this amine compound, the amine compound is removed by washing the carbon dioxide obtained through the decarbonation with washing water (see, for example, Patent Document 5: Japanese Patent Application Laid-open No. 2002-126439). However, in the case of using such an amine compound as a carbon dioxide absorbent, in most cases, the absorbent is used as an aqueous solution, and hence it is known that the carbon dioxide obtained through the decarbonation step contains water (see for example, Patent Document 5: Japanese Patent Application Laid-open No. 2002-126439), and furthermore in the case that an aqueous washing step for removing amine compound present as an impurity is added, the water content of the carbon dioxide is yet further increased.
On the other hand, in the case of using a solid absorbent such as calcium hydroxide or a zeolite as the absorbent, the absorbent must be made into a fine powder so as to increase the contact area, but there has been a problem that such a fine powder is difficult to handle. Methods in which this problem is resolved have been reported, for example a method using a lithiated oxide is known (see for example, Patent Document 6: Japanese Patent Application Laid-open No. 2002-85966). However, with this method, each of the carbon dioxide gas absorption and elimination must be carried out at a temperature of several hundred degrees, and hence there has been a problem that much energy must be inputted for the carbon dioxide recovery. That is, many methods have been known hitherto, but many problems remain with such processes in which carbon dioxide gas is absorbed and recovered, and then eliminated to obtain carbon dioxide gas.
A case in which carbon dioxide is inserted into a tin-methoxide linkage of dimethyltin dimethoxide has been reported (see, for example, Non-Patent Document 1: J. Am. Chem. Soc., 121 (1999), 3793-3794). In this case, it is stated that the matter in which the carbon dioxide is inserted into the dimethyltin dimethoxide is present in supercritical carbon dioxide, and that carbon dioxide is produced in an excess (in this case, 4 equivalents) based on the tin atoms contained in the dimethyltin dimethoxide. Furthermore, it is stated that there is production even with a 4° C. saturated carbon dioxide solution, but it is stated that at the same time the product is unstable at room temperature with carbon dioxide being discharged, and hence carbon dioxide recovery and reuse has not been accomplished.
Furthermore, a case in which carbon dioxide is inserted into a tin-methoxide linkage of 1,3-dimethoxytetrabutylstannoxane has been reported (see, for example, Non-Patent Document 2: Applied Catalysis A: General, 255 (2003), 93-99). In this case, the 1,3-dimethoxytetrabutylstannoxane is reacted with carbon dioxide at room temperature and atmospheric pressure so as to obtain solid 1-methoxy-3-methylcarbonatetetrabutylstannoxane. However, this solid is produced only in structural identification, and a method in which the solid is utilized has not been accomplished. As an example in which the reaction product between 1,3-dimethoxytetrabutylstannoxane and carbon dioxide is utilized, there is a method previously disclosed by the present applicants (see, for example, Patent Document 9: WO 03-055840), but this is merely the method in which the 1,3-dimethoxytetrabutylstannoxane is put into a high pressure vessel and reacted with carbon dioxide, so as to produce a carbonate in the high pressure vessel. The present invention is a result of further assiduous studies with an objective of realizing a composition for recovery utilization and/or transfer by making a specified tin compound contain carbon dioxide in a specified ratio, and is completely different to the above art.
Related to the above, in recent years there have been disclosed carbonate production processes in which carbon dioxide is used as a starting material (see, for example, Patent Document 8: Japanese Patent No. 3385359, Patent Document 9: WO 03-055840). In such a carbonate production processes in which carbon dioxide is used as a starting material, the reaction equilibrium is biased to the reactant system side, and hence in general high-pressure carbon dioxide is used, and in many cases supercritical carbon dioxide is used (see, for example, the examples in Patent Document 8: Japanese Patent No. 3385359); the amount of carbon dioxide used in the reaction is very low, unused carbon dioxide being discharged. Moreover, the present inventors have disclosed a method in which the carbon dioxide is not made to be supercritical but rather carbon dioxide at a relatively low pressure is used (see, for example, Patent Document 9: WO 03-055840), but it is merely stated that if the carbon dioxide is subjected to reaction at high pressure then the carbon dioxide goes to waste upon returning to normal pressure, and there are no cases in which recovery and reuse of the unreacted carbon dioxide is described.
The carbon dioxide discharged from such a carbonate production process in which carbon dioxide is used as a starting material is at normal pressure; as a process for reusing such carbon dioxide discharged at normal pressure, an example is a method in which the carbon dioxide is used after having been re-pressurized using a compressor or the like as used in a supercritical carbon dioxide extraction system. With this method, the carbon dioxide at approximately normal pressure must be pressurized to at least several MPa. As compared to the carbon dioxide used in the reaction, there is much more unreacted carbon dioxide that is discharged and must be re-pressurized (in many cases at least several tens of times as much), and hence a very large compressor is required, and moreover much electrical energy must be inputted to drive the compressor and to use a cooler to remove heat produced when compressing the carbon dioxide. This equipment and input of electrical energy causes a worsening of the cost competitiveness of the carbonate production, so that the carbonate production is not worth implementing industrially, and hence the above has not been implemented as a carbonate production process. Moreover, in the case that the reaction system contains a low-boiling alcohol (e.g. methanol) or a low-boiling carbonate (e.g. dimethyl carbonate), the carbon dioxide discharged from the high pressure state contains much of this low-boiling alcohol or low-boiling carbonate, and hence this low-boiling matter (low-boiling alcohol or low-boiling carbonate) may partially liquefy when the discharged carbon dioxide is re-pressurized, and to maintain the compressor performance, it may be necessary to control withdrawal of the liquefied low-boiling matter, so that the apparatus for maintaining the compressor performance becomes very difficult.
Patent Document 1: Japanese Patent No. 2809368
Patent Document 2: Japanese Patent Application Laid-open No. 2003-261315
Patent Document 3: Japanese Patent Application Laid-open No. 5-184864
Patent Document 4: Japanese Patent Application Laid-open No. 2004-344703
Patent Document 5: Japanese Patent Application Laid-open No. 2002-126439
Patent Document 6: Japanese Patent Application Laid-open No. 2002-85966
Patent Document 7: Japanese Patent Application Laid-open No. 2003-192643
Patent Document 8: Japanese Patent No. 3385359
Patent Document 9: WO 03-055840
Non-Patent Document 1: J. Am. Chem. Soc., 121 (1999), 3793-3794
Non-Patent Document 2: Applied Catalysis A: General, 255 (2003), 93-99